There is an increasing concern with the environmental impact of waste. More particularly there is a concern with the use of non-degradable material such as petroleum based plastics. There has been for some time knowledge of degradable polymers based on lactides. Generally these polymers have been produced either by a fermentation process or by the direct polymerization of lactic acid. Such polymers have had very little impact on the field of plastics due to cost and monomer supply considerations. There is now a renewed interest in such polymers. However, when lactic acid is polymerized there is a tendency for it to form dimers or lactides. This tends to reduce yield, slow the rate of reaction and result in polylactides having a low molecular weight or a low intrinsic viscosity in the neighbourhood of less than 0.1 dl/g as measured as a 0.5% solution of polymer in a solvent such as chloroform.
WO 90/01521 published Feb. 22, 1990 in the name of Battelle Memorial Institute contains a good review of the history of such polymers and a good outline of the prior art.
U.S. Pat. No. 4,045,418 issued Aug. 30, 1977 assigned to Gulf Oil Corporation discloses the copolymerization of lactic acid and caprolactone. Additionally the patent discloses the polymerization of lactic acid with 4-valerolactone and delta valerolactone. The disclosure of the patent concludes that the only copolymerizable monomer in addition to caprolactone is delta - valerolactone (Col. 3, lines 60 through 69). The 4-valerolactone did not polymerize at all. As such the teaching of U.S. patent goes against the subject matter of the present invention.
The present invention seeks to provide a co- or ter polymer of lactic acid which contains 4-valerolactone.